The ability of the organism to respond to stress is integrated by the nervous and endocrine systems. Specifically, the underlying anatomical structures consist of the hypothalamus, the pituitary, and the adrenal glands. When the organism is stressed, the hypothalamus secretes corticotropin releasing factor (CRF) which controls the release of adrenocorticotropin (ACTH) and beta-endorphin from the pituitary gland. ACTH controls adrenocorticosteroid release which is necessary during stress. This study will examine the effect of time of day, prior stress and type of stress on the time course of the stress response in Sprague Dawley rats. Radioimmunoassay (RIA) will be used to measure hypothalamic corticotropin releasing factor like immunoreactivity (CFR-LI), extrahypothalamic CRF-LI, plasma ACTH, beta-endorphin and corticosterone levels. Intraperitoneal injection and exposure to ether vapors will be used as low intensity, short duration stresses and restraint stress will be used as an example of a high intensity, long duration stress. Also gel filtration chromatography or high performance liquid chromatography (HPLC) will be used to investigate the different molecular weight forms of CRF that occur during the time course of the stress response. This study will provide insight into the physiological significance of CRF-41 and its role in integrating the organism's ability to respond to stress.